An internal combustion engine to drive a ship or motor vehicle is operated using a broad load and rotational speed range, where the lowest fuel consumption by the internal combustion engine is attained in a very narrow rotational speed and torque range. The surface of the fuel consumption map is characterized as a range of minimum consumption. Outside of the range of minimum consumption, the internal combustion engine operates with unfavorable efficiency and, thus, high fuel consumption. So-called hybrid drives were developed with the goal of fuel savings, in which an internal combustion engine was combined with at least one electric machine, wherein along with a fuel tank for the internal combustion engine, a battery is provided for storing electrical energy. Here a battery is understood to be any electrical energy storage, including, for example capacitive storage. With a hybrid drive system, because the internal combustion engine can be decoupled from the output drive, it is possible to operate the internal combustion engine as required in or near the range of minimum consumption in its fuel consumption map. For other driving conditions, the output drive occurs using the electric machine. Furthermore, in a hybrid drive system, energy recovery or energy recuperation is possible; as a result of the mechanical connection of the output drive and the electric machine, in certain operating conditions, such as during braking or downhill travel of motor vehicles, the electric machine can be driven from the output drive side. Regenerative energy generation is possible with ships too, using solar energy or wind energy. In a motor ship it is possible to utilize the wind energy only using a wind turbine; in contrast, in an application as a drive of a sailing ship, such recuperation can occur using the drive of the electric machine acting as a generator in sailing mode by using the propeller acting as a turbine. Furthermore, it is possible to use the flow energy of the water flowing around the ship in both a motor ship as well as in a sailing ship in flowing waters. The generated electrical energy can be used directly or stored in an electrical energy accumulator. Even sailing ships depend on a drive under specific situations, such as during calm conditions or during docking and casting-off maneuvers. The drive can then occur using a hybrid drive system, alternatively electrically or using an internal combustion engine or a combination of the two.
A ship drive is known which is designed as a so-called “diesel-electric” drive. In this case, an internal combustion engine drives a generator; electrical energy generated by this generator drives an electric motor. The electric motor, in turn, drives a propeller shaft. With this, the internal combustion engine is mechanically decoupled from the propeller shaft, and can be operated advantageously with the drive of a generator in normal mode or close to the minimum consumption range. Furthermore, the arrangement of the internal combustion engine is not connected to the propeller shaft, and can be disposed practically anywhere in the ship's hull.
A disadvantage of this diesel-electric drive is that at low speeds, the internal combustion engine can only be operated at low load, and therefore no longer in the range of minimum consumption. The double energy conversion is a further disadvantage, as are the conversion losses associated with it. In the ideal case, the internal combustion engine can be driven constantly in its minimum consumption range, however the conversion in the generator of mechanical energy into electrical energy, and the subsequent conversion in the electric motor of electrical energy into mechanical energy reduces efficiency. Through these losses, the consumption advantage of the internal combustion engine driven statically in the range of minimum consumption can be reduced or overcompensated.
Strictly speaking, according to the definition, this is not a real hybrid drive system because there is no possibility of storing the electrical energy generated by the generator. As a result, the internal combustion engine must be operated constantly to drive the propeller, and this is associated with all of the negative effects such as exhaust and noise emissions. In an application in a sailing ship, the electrical energy accumulator cannot be charged during sailing mode or using flows.
Furthermore, a so-called “serial hybrid drive” of a ship is known from the prior art, whose design is similar to that of the diesel-electric drive. However, the serial hybrid drive, in addition to the generator and electric motor, also has a battery as a storage possibility for the electrical energy generated by the generator. As a result, more drive variants are possible. Thus, during normal travel or with heavy loads or at high ship speeds, the drive uses “diesel-electric” because the internal combustion engine can be operated in its minimum consumption range under these operating conditions. The internal combustion engine can also be arranged anywhere within the ship's hull.
As with the diesel-electric drive, a disadvantage of the serial hybrid during normal travel is the double energy conversion and the resulting conversion losses associated with it. Due to these losses, the consumption advantage of the internal combustion engine operating statically in the minimum consumption range can be reduced or overcompensated.
If the internal combustion engine is not utilized completely to capacity by the propeller drive, the battery can be charged using the excess torque. With low load or at slow ship speeds, the internal combustion engine is switched off, and the propeller is driven using the electric motor supplied by the battery. The purely electric drive of the ship offers additional advantages of emission-free maneuvering in the harbor, and makes it possible to operate in an environmentally friendly manner with respect to exhaust and noise emissions. The internal combustion engine is only switched on again to charge the battery when it falls below a specific charging state.
For a sailing ship, the described hybrid drive system makes it possible to charge the battery while sailing or to generate current, in that the propeller acts as a turbine, and the electric machine, operated as a generator, provides the drive. Additionally, it is also possible to charge the battery from the power network while in port. The hybrid drive system is monitored and controlled by an electronic control unit.
A further variant of a hybrid drive system for a ship is the so-called “parallel hybrid drive system”. In contrast to the serial hybrid drive system, in this case the internal combustion engine is not mechanically decoupled from the propeller. The parallel hybrid drive system comprises an electrical energy accumulator, for example a battery, and an electric machine operating, according to control, only as an engine or generator in contrast to the serial hybrid and the diesel-electric drive. Furthermore, the parallel hybrid drive system has a mechanical switchgear which consists of an arrangement of clutches, for example. The drive can occur electrically, or using the internal combustion engine, or using a combination of the two.
Different operating modes of the drive can be set using the mechanical switchgear and its control by an electronic control unit. Thus, the internal combustion engine can drive the propeller directly, which preferably occurs in those operating states in which the internal combustion engine operates in or near the minimum consumption range, for example during normal travel or at high required drive torques. In comparison to the serial hybrid, there are no losses in efficiency as a consequence of a mechanical-electrical-mechanical energy conversion. If the internal combustion engine is not completely loaded with the drive of the propeller, in a further setting of the mechanical switchgear and power electronics, the internal combustion engine can drive the electric machine in the generator mode and charge the battery. If the ship is moving at slow speed or in maneuvering mode, or if the surroundings require quiet and exhaust-free operation, then the mechanical switchgear produces only the mechanical connection between the electric motor and propeller. The internal combustion engine is now switched off. In this switch setting of the mechanical switchgear, it is also possible with appropriate control by the electronic control unit that in sailing mode the propeller acts as a turbine and drives the electric machine as a generator in order to charge the battery. An environmentally friendly and renewable energy source is possible using this so-called recuperation. In the process, the internal combustion engine can be switched off. In a further mode of operation in which short-term high drive power is required, due to the switch setting of the mechanical switchgear, both the internal combustion engine and the electric motor can act on the propeller and thus add their power (“boost” mode). As a result, with the same maximum drive power as in the mode using purely the internal combustion engine, the internal combustion engine can be unloaded by the additional power from the electric motor, or a peak need of drive power can be covered.
A parallel hybrid drive system for a ship is known from the document SI 22377A; this parallel hybrid drive system has an electric machine with a first clutch, a battery, an electronic control unit and a drive unit with a second clutch and a converter charging unit. In this case, the first clutch is disposed between the internal combustion engine and the electric machine, and the second clutch is disposed between the electric machine and the propeller shaft.
The “Integrated Starter Motor Generators” catalog from Iskra Avtoelektrika, the owner of the document SI 22377 A, shows a ship drive system that has a parallel hybrid drive system such as that of SI 22377 A, and comprises a rear drive as a drive device. In the rear drive, a double redirection of the drive train to the propeller occurs using two V drives. The first clutch is designed as a multi-disk clutch or claw clutch. The following operating modes can be set using this parallel hybrid drive system: in a start mode, the first clutch is engaged and the second clutch is disengaged. In this case, the electric machine acts as a starter and places the internal combustion engine in gear. As soon as the internal combustion engine is running, the drive system automatically switches by means of the electronic control unit into the generator mode, in which likewise the first clutch is engaged in the second clutch is disengaged. The internal combustion engine drives the electric machine acting as a generator, and charges the battery. Optionally, while the ship is in port, the battery can be charged from the power network using a converter charging unit of the power electronics. In the electric drive mode, the first clutch is disengaged and the internal combustion engine is stopped. The second clutch is engaged so that the electric machine, now acting as a motor, drives the propeller. In a so-called boost mode, both clutches are engaged and the electric machine and the internal combustion engine operate in parallel. The sum of the drive power from both machines drives the propeller.
A reversal of the propeller direction, which is necessary for reversing the direction of travel of the ship during docking and casting-off maneuvers, for example, is attained with the rear drive shown by shifting the double cone clutch. This shifting is only possible however, if the direction of rotation of the electric machine corresponds with that of the internal combustion engine. If the reversal of the direction of rotation of the propeller in the purely electric mode is to occur by an easy to implement reversal of rotation of the electric machine, the double cone clutch, due to its constructive design, disengages like a freewheel, and disadvantageously cannot transfer any drive torque to the propeller. Therefore, the second clutch cannot be shifted at will, and in this sense in not a clutch.
Hydraulically actuated clutches, which are also used in rear drives or ship drives with undeflected drive trains, have several disadvantages. In the event of a leak for example, operating media, which is environmentally hazardous and critical to operational safety, can leak out of hydraulic lines and machines. In addition, in order to generate oil pressure, a hydraulic system requires at least one pump that is an additional component and that uses part of the drive power generated by the ship's drive, which, in purely electric mode, requires energy from the battery and therefore shortens the possible runtime of the electric machine. If the pump is mechanically driven by the electric machine, it is not possible to reverse the direction of rotation of the electric machine because in most displacement pumps, reversing the direction of rotation also reverses the direction of conveying. Pumps that are independent of the direction of rotation, such as radial piston pumps, are complex and expensive. For this reason, the direction of rotation of the electric motor driving the pump cannot be changed even in electric mode, so that a mechanical switching of the direction of rotation of the pump is required. Although a pump driven by its own electric motor (e-pump) can function independently of the direction of rotation of the electric machine, an e-pump is complex and due to the double conversion of energy, operates at a poor degree of efficiency.
As a further disadvantage, the rotational speed of the electric motor can only be lowered to a minimum rotational speed at which the pump still conveys the operating media and can generate pressure. As a result, a major advantage of the electric drive during maneuvering, or docking and casting-off is nullified, and convenience is compromised.
The document EP 1 914 161 A2 shows a parallel hybrid drive system for ships. No second clutch is disposed between an electric machine acting as an electric motor and drive mechanism or propeller. Generating electrical current by operating the electric machine only as a motor is not possible; a separate generator is provided for this, which means additional expenditures of construction space, cost and weight.
The document EP 1 669 287 A1 does not disclose a clutch between the internal combustion engine and electric machine. A shiftable clutch for switching the direction of rotation of the propeller is present in the drive mechanisms. A purely electric drive is disadvantageously not possible.
The patent application US 2008/0113570 show an outboard motor as a hybrid drive system for a ship which has an internal combustion engine, an electric motor acting also as a generator and a drive mechanism. A claw clutch is needed to reverse the direction of rotation of the propeller in order to change the direction of travel.